1. Field of the Invention
The present invention relates to a new and improved process for the preparation of alkyl- or arylphosphonothioic dihalides.
2. The Prior Art
Alkylphosphonothioic dihalides have been prepared in the prior art by reacting alkyl halides with phosphorus trihalides in the presence of aluminum chloride. The reaction proceeds at room temperature according to the formula set forth in Heuben-Weyl, Methoden der Organis Chenchemie, Volume 12, part 1 (1965) at page 396. ##STR1## The Heuben-Weyl reference also notes that the reaction has been attempted in the absence of the aluminum chloride catalyst with little success. The alkylphosphonothioic dihalides are prepared by replacing the oxygen of the alkylphosphonic dihalide with sulfur as shown on page 553 of the Heuben-Weyl reference. The yields of the replacement reaction are limited to the yields obtained in the initial reaction forming the alkylphosphonic dihalide.
Other known methods of preparing alkylphosphonothioic dihalides are described in Journal of the American Chemical Society, 88 3041 (1966).
Alkyl- and arylphosphonothioic dihalides also can be prepared according to our U.S. Pat. No. 3,790,629 by reacting an aliphatic hydrocarbon with a pentavalent thiophosphorus compound having at least two halogens attached thereto under at least autogenous pressure at a temperature of from 200.degree. C. to 450.degree. C.
Cycloalkanephosphonothioic dichlorides have also been prepared by reacting a cycloalkene with thiophosphoryl chloride under irradiation with mercury lamps. Reaction times are long and low yields are reported (Angew, Chem. Internat. Edit., Vol. 9 (1970), No. 6 at p. 458).
Phosphorus trihalide and elemental phosphorus are wellknown and are readily available commercially.